In view of the significant price increases in petroleum oils in the last few years along with the increased demands for turbine fuels and particularly aircraft fuels, renewed attention has been focused on the recovery of oil from sources other than crude oil such as oil shale, coal and the subsequent conversion of the oil sources to usable, valuable, combustible transportation fuel products and particularly jet fuel products.
A number of differences exist between various petroleum oils depending on source and oils derived from oil shale, coal and crude oil. One significant difference is the amount of various sulfur, nitrogen and metal contaminants present in the oil. Petroleum oils contain up to about 0.05% by weight of nitrogen, whereas shale oils generally contain at least about 0.5% and mainly at least about 1% by weight of nitrogen. These quantities of nitrogen if not significantly reduced prior to catalytic processing such as by catalytic reforming and catalytic cracking can cause significant processing problems. The nitrogen tends to poison and/or reduce catalyst activity used in such processes. In addition, the burning of oils containing such quantities of nitrogen as well as sulfur is a problem from an ecological viewpoint, since the burning produces nitrous oxide and sulfur oxides. Only very restricted amounts of such oxide are permitted to be exhausted into the atmosphere. Furthermore, the presence of nitrogen in the finished fuel is undesirable since nitrogen compounds tend to cause thermal instability of the finished fuel.
One method employed to reduce the nitrogen content of heavy oils obtained from crude oil and shale oil has been to subject the shale oil to hydrotreating using a suitable hydrogenation catalyst. However, such processes in order to remove sufficient quantities of bound nitrogen have required relatively severe hydrogenation operations of high hydrogen consumptions such as up to 3000 standard cubic feet per barrel (SCF/B) and more generally at least about 1200 SCF/B of hydrogen at relatively high temperatures and pressures. Accordingly, such processes have been quite expensive in order to reduce the nitrogen component to an acceptable low level to withstand the temperature and pressure conditions found necessary.
The use of various acids such as sulfuric, hydrofluoric, hydrochloric, nitric and phosphoric acid to extract nitrogen compounds from oils has been suggested by the prior art, but have been less than completely satisfactory because of hydrogen consumption and an oil product yield of less than desired volume. This unsatisfactory condition is also due in part to the fact that, not all of the nitrogen compounds as initially contained in the oil feed are considered basic nitrogen compounds or are extractable with mineral acids, and particularly, all are not extractable with the acid particularly desired to be employed according to the present invention. For instance, Chemical Abstracts Vol. 44-7518(d) describes at least three classes of nitrogen compounds which are recognized as being contained in crude shale oil. Besides basic nitrogen compounds which are extractable with relatively weak acids, crude shale oil also contains varying amounts of nitrogen compounds which are insoluble in weak acids, and which are polymerized by strong acids; and compounds which are stable for example to concentrated sulfuric acid and are not extracted thereby. Accordingly, various processes have been suggested in the prior art employing different acids in combination with other treating steps as discussed below with varying degrees of success.
For instance, U.S. Pat. No. 2,692,226 to Smith suggests treating shale oil by hydrogenation with a catalyst composed of a mixed sulfide of nickel and tungsten or nickel and molybdenum. The hydrogenation employed is relatively severe as shown by the reaction conditions employed. The hydrogenation as suggested by Smith results in a substantial removal of the nitrogen content of the oil as illustrated in the table on column 3 thereof. Smith further suggests treating the hydrogenated material to improve its color by a mild acid treatment with sulfuric acid. The hydrotreating step suggested by Smith should be severe enough so as to saturate aromatics and olefins to prevent the loss in yield discussed therein. Sulfuric acid tends to cause polymerization of the olefins and to remove the aromatics along with nitrogen compounds. Accordingly, Smith seems to suggest that a large portion of the nitrogen could not be removed by the acid treatment without a great loss in yield. Nowhere does Smith suggest any preference for phosphoric acid, and in fact, the use of sulfuric acid therein tends to suggest a preference for sulfuric rather than phosphoric acid. Moreover, Smith does not indicate that the use of phosphoric acid would provide different results than sulfuric acid.
U.S. Pat. No. 3,085,061 to Metrailer suggests a process for refining shale oil which includes a mild hydrotreatment to remove sulfur followed by treatment with anhydrous hydrogen chloride to form a sludge containing substantially all of the nitrogen. Metrailer further suggests that solvents previously employed in shale oil refining which removed undesirable nitrogenous materials were unselective and removed desirable cracking constituents as well. Accordingly, Metrailer would tend to lead persons skilled in the art away from the present invention since among other things it would be contrary to the suggestions of Metrailer to employ an aqueous phosphoric acid system.
Besides Metrailer, there exists a number of other prior art patents which would tend to lead persons skilled in the art away from the phosphoric acid employed according to the present invention. For instance, U.S. Pat. No. 3,309,324 to McAllister et al. suggests the use of certain weak acids to extract nitrogenous compounds from various oils. McAllister et al. suggest that the use of strong mineral acids such as sufuric acid and hydrochloric acid results in certain disadvantages. These disadvantages suggested by McAllister et al. include the tendency of the strong acids to polymerize unsaturated hydrocarbons which are frequently present in petroleum distillates, and to extract constituents which because of their anti-knock prospects are more advantageously left in for motor fuels. The present invention does not suffer from these disadvantages.
U.S. Pat. No. 2,966,450 to Kemberlin, Jr. et al. suggests a process for refining shale oil which includes using a selective solvent and anhydrous hydrogen chloride. Kemberlin, Jr. et al. suggests that solvents previously employed in shale oil refining, including strong acids such as sulfuric acids and weak acids such as sulfurous acid gave unsatisfactory results, either because of ineffectiveness or poor selectivity, (e.g. resulting in removal of desirable cracking constituents along with the nitrogenous materials).
U.S. Pat. No. 2,662,843 to Castner et al. suggests a process for refining shale oil which includes using formic acid preferably after a mild thermal cracking. Castner et al. further suggests that solvents previously employed in general were not sufficiently selective and removed desirable substances such as aromatics.
U.S. Pat. No. 2,541,458 to Berg suggests aqueous solutions of various volatile acids or salts of non-volatile acids to recover nitrogen bases from shale oil but does not specifically suggest employing non-volatile acids such as phosphoric acid required by the technique of the present invention, and does not suggest cracking a portion of the oil feed prior to acid extraction of basic nitrogen components to extend the yield of desired turbine fuel products.
U.S. Pat. No. 2,518,353 to McKinnis suggests removal of nitrogen compounds from oils including shale oil and shale oil fractions with an extractant containing acid, ammonium or amino or salts of strong non-volatile acids, such as salts of phosphoric acid. The examples of said patent suggest mixtures of free phosphoric acid with the required extractant compounds. However, this patent would actually tend to lead persons skilled in the art away from the present invention since among other things there is no suggestion in this patent to employ a mild hydrogenation step before a restrained catalytic cracking step and prior to the particular acid extraction of the nitrogen compounds as disclosed by the present invention.
The discussion in Chem. Abstracts 44-7518(d) suggests the removal of certain nitrogen compounds from shale oil employing dilute mineral acids. However, such limited disclosures does not remotely suggest the integrated combination process of this invention comprising a restrained catalytic cracking step prior to acid extraction and subsequent reforming of a mildly hydrogenated product thereof as required by the present invention.
U.S. Pat. No. 3,123,550 to Skomoroski et al. suggests mixing a shale oil distillate with an acid such as phosphoric acid, and then hydrotreating the mixture. The acid is suggested as aiding in increasing the catalyst surface available for hydrogen adsorption (see column 1, lines 49-61 for instance).
U.S. Pat. No. 2,035,583 to Bailey suggests a process for separating and purifying nitrogen bases which includes use of various acids. However, there is no disclosure of the phosphoric acid extraction steps in the integrated combination process according to the present invention.
U.S. Pat. No. 2,084,617 to Chellis et al. is concerned with reducing the nitrogen content of naphthas prior to reforming. Chellis et al. suggest mild hydrotreating followed by treatment with sulfuric acid followed by mild hydrotreating followed by another treatment with sulfuric acid, which latter process is preferred by Chellic et al. for shale oil naphthas.
U.S. Pat. No. 2,800,427 to Junk, Jr. et al. suggests pretreating hydrocarbon oils prior to catalytic cracking with a non-oxidizing acid such as sulfuric acid and hydrochloric acid.
U.S. Pat. No. 2,925,381 to Fleck et al. suggests removing organic nitrogen compounds from hydrocarbons such as shale oil by using a zeolite.
An object of this invention is to improve the production of jet fuel, particularly military jet fuel, from one or a combination of oil fractions such as shale oil, an oil product of coal processing and select crude oil fractions under conditions of low cost and minimum consumption of hydrogen. Jet fuels suitable for military use have a number of specific properties which must be met.
The specific properties include an API gravity restriction, volumetric distillation temperatures including initial and end boiling points, freeze point, flash point, luminoscity number, thermal stability, aromatic concentration, the IPT smoke point, the analine point and the concentration of sulfur and nitrogen contaminants.
A series of complex processing operations are required to achieve these desired jet fuel properties which vary with jet fuel desired, JP4, JP5, JP8, etc. A further object of this invention is to maximize the yield of jet fuel from the oil feed by providing a process combination which facilitates the economic production of the turbine fuel product desired in high yields from distress stocks. Certain jet fuels have a very low initial boiling point with an end point specified to fall within the range of 350.degree. up to about 450.degree. F. Other turbine fuels have a higher initial boiling point with an end boiling point of at least about 550.degree. F. or greater. In the combination process of this invention a separated initial hydrotreated product has an end point within the range of 500.degree.-650.degree. F. separated from higher boiling material subsequently cracked as herein provided in order to obtain as much jet fuel as possible from selected oil feeds; such as JP4, JP5 and JP8, jet fuels or others. Conversion of a broad range of feed stock to form jet fuels is extremely desirable during periods of crude oil scarcity, military emergency and/or for other fuel purposes.